JP2006108161A - Semiconductor light-emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly luminous semiconductor light-emitting device capable of limiting an interfacial reaction between a metal reflection film and a transparent conductive film, capable of improving the reflection rate of a metal reflection layer, and capable of improving external quantum efficiency of the semiconductor light-emitting device by forming an insulating protective film between the metal reflection layer and transparent conductive film. <P>SOLUTION: In the flip-chip type group III nitride based compound semiconductor light-emitting device, the transparent conductive film 10 comprising an ITO is formed on a p-type contact layer, the insulating protective film 20 is formed thereon, a reflection film 30 comprising silver (Ag) and aluminum (Al) for reflecting light toward a sapphire substrate is formed thereon, and the metal layer 40 comprising gold (Au) is formed thereon. Since the insulating protective film 20 is interposed between the transparent conductive film 10 and the reflection film 30, the diffusion is prevented in metal atoms constituted by the reflection film 30 to the transparent conductive film 10. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor light emitting device. In particular, the present invention relates to a flip-chip light emitting element that emits light from the side of a light-transmitting substrate, which has improved external quantum efficiency, and which has prevented deterioration over time.

  Conventionally, as shown in Patent Document 1 below, a flip-chip type semiconductor light emitting device using a group III nitride semiconductor double heterojunction structure is known. In the light-emitting element, a sapphire substrate is used as a light-transmitting substrate, and an electrode layer made of rhodium (Rh) functioning as a reflection layer and a current supply electrode is provided on the uppermost p-type contact layer. Then, of the light emitted from the light emitting layer by this electrode layer, the light directed to the opposite side of the substrate is reflected to the substrate side, and the light is effectively output to the outside. Rhodium has a relatively high value of 60% reflectivity for blue light. On the other hand, silver, aluminum, or a silver alloy has a reflectance of 60% or more and is useful for use as a reflective layer. However, when silver or aluminum is subjected to a heat treatment such as an alloy with respect to the p-type contact layer, the reflectance is lowered due to discoloration or alteration. In particular, in the case of using silver, there is a problem that it is easily peeled off from the p-type contact layer. Also, since ion migration and electromigration are remarkable, there are problems in electrical and reliability. There is.

  These are also found in GaAs semiconductors as shown in Patent Document 2 below, and in order to solve this, a transparent indium tin oxide (ITO) is formed on the contact layer. A reflective layer made of Au or Au / Cu is formed thereon so that the metal does not react directly with the semiconductor layer.

Further, in Patent Document 3 below, an ITO film is formed on a GaN-based semiconductor layer in order to improve the external quantum efficiency of the flip-chip type light emitting device, and a reflective layer such as silver or aluminum is formed thereon. Is disclosed.
JP 2000-36619 A JP 10-4208 Actual climb 3068814

  However, when a reflective layer made of silver or aluminum is formed on the ITO film, the ITO, silver, or aluminum is altered or discolored by the interface reaction, and the amount of light incident on the metal reflective layer The present inventors have found that the light that is reflected to the substrate side and extracted outside is reduced.

  The present invention has been made to solve these newly discovered problems, and its purpose is to form an insulating protective film between a metal reflective layer and a transparent conductive film, It is to suppress the interface reaction between the reflective film and the transparent conductive film, improve the reflectance by the metal reflective layer, and improve the external quantum efficiency of the semiconductor light emitting device.

The configuration of the invention for solving the above-described problems is as follows.
The invention of claim 1 has a light-transmitting substrate and a semiconductor layer laminated on the light-transmitting substrate, and an n-electrode and a p-electrode are on the semiconductor layer side with respect to the light-transmitting substrate. In a flip-chip type semiconductor light emitting device that emits emitted light from the translucent substrate side, the contact layer that is the uppermost layer of the semiconductor layer, and transparent to the light formed on the contact layer A transparent conductive film, an insulating protective thin film formed on the transparent conductive film, a reflective film having a high reflectance with respect to emitted light made of a metal formed on the insulating protective film, and the reflective film And an electrode layer formed so as to be bonded to a part of the transparent conductive film.

  Here, the light emitting element is a flip chip type semiconductor light emitting element used in a so-called face down in which the semiconductor layer side is bonded to the lead frame with the substrate facing up. The material of the semiconductor is arbitrary, but the present invention is particularly effective when used for a group III nitride semiconductor light emitting device. The contact layer on which the transparent conductive film is formed may be either a p-type semiconductor or an n-type semiconductor. In the case of a group III nitride semiconductor, the uppermost layer farthest from the translucent substrate is usually a p-type semiconductor because of the p-type treatment, but the uppermost layer is an n-type semiconductor due to the evolution of manufacturing technology. Therefore, the present invention is applicable to any contact type of the contact layer on which the transparent conductive film is formed.

Any translucent substrate may be used as long as it has a high transmittance with respect to the light emitted from the light emitting layer. For example, sapphire (Al ₂ O ₃ ), silicon carbide (SiC), gallium nitride (GaN), gallium phosphide (GaP), zinc oxide (ZnO), magnesium oxide (MgO), manganese oxide (MnO), general formula Al quaternary represented by _{x Ga y in 1-xy N} , 3 -way, it is possible to use a binary semiconductor. In short, any material having a high transmittance with respect to the emitted light may be used.

Examples of the transparent conductive film include metal oxides. Typically, indium tin oxide (ITO) or zinc oxide (ZnO) is preferably used.
Examples of the insulating protective film include metal oxide, metal nitride, and glass. Typically, silicon oxide (SiO, SiO ₂ , Si _x O _y, etc.), silicon nitride (SiN, Si ₂ N ₃ , Si _x N _y ), titanium oxide (TiO, TiO ₂ , Ti _x O _y, etc.), titanium nitride (TiN, TiN ₂ , Ti _x N _y, etc.), or a composite of these or a laminate thereof Such as a membrane.
The reflective film may be any metal as long as it has a high reflectance with respect to the emitted light. Desirably, silver (Ag), aluminum (Al), a silver alloy, an aluminum alloy, an alloy containing silver and aluminum as main components, and the like are preferable.
The material of the electrode layer is arbitrary, but gold, a multilayer film of gold and titanium, or an alloy of gold and titanium can also be used.

  According to a second aspect of the present invention, the transparent conductive film has an exposed portion where an insulating protective film is not formed on at least a part of its peripheral portion, and a part of the electrode layer is provided on the exposed portion. The semiconductor light emitting device according to claim 1, wherein the semiconductor light emitting device is a semiconductor light emitting device.

  The exposed portion is formed by the relationship between the transparent conductive film and the insulating protective film formed thereon. Even if the exposed portion is provided over the entire periphery of the peripheral portion of the transparent conductive film, the exposed portion may be formed in a part of the periphery or in a plurality of surrounding regions. And since an electrode layer will join this exposed part, an electrode layer will be in electrical contact with a transparent conductive film in this exposed part, and an electric current is supplied from this part.

  The invention according to claim 3 is the semiconductor light emitting element according to claim 1 or 2, wherein the periphery of the reflective film is covered with an insulating protective film. That is, by forming the reflective film in the insulating protective film, reactions at the interface between the reflective film and the transparent conductive film and at the interface between the reflective film and the electrode layer can be completely suppressed. Moreover, when electromigration is remarkable as in the case where the reflective film is made of silver, this can be completely suppressed, and a decrease in reflectance can be prevented.

  The inventions of claims 4 to 7 have been described as desirable examples with respect to the invention of claim 1.

  The interfacial reaction between the reflective film and the transparent conductive film is suppressed by the insulating protective film. For this reason, the fall of the transmittance | permeability of a transparent conductive film and the reflectance of a reflecting film can be prevented. Therefore, the extraction efficiency of the light output to the outside through the translucent substrate is improved.

When energizing, the current flows into the transparent conductive film only from the contact portion between the electrode layer and the transparent conductive film due to the presence of the insulating protective film. For this reason, the possibility of occurrence of electromigration in the reflective film can be greatly reduced. When the entire reflective film is covered with an insulating protective film, the electromigration of the reflective film can be further prevented.

The best mode for carrying out the present invention will be described.
A specific layer configuration of the semiconductor light emitting element will be described in detail in a later example, but the present invention is a flip chip type semiconductor light emitting element 1 as shown in FIG. Light is output to the outside from the translucent substrate 101 side. On the translucent substrate 101, a semiconductor layer made of a group III nitride semiconductor is laminated, and the uppermost layer is the contact layer 108. On the contact layer 108, a transparent conductive film 10, an insulating protective film 20, a reflective film 30, and an electrode layer 40 are sequentially formed.

  The contact layer 108 has an annular first exposed portion 5 on which the transparent conductive film 10 is not formed on the peripheral portion. In addition, the transparent conductive film 10 has an annular second exposed portion 11 in which the insulating protective film 20 is not formed on the upper surface in the peripheral portion. Furthermore, the insulating protective film 20 has an annular third exposed portion 21 on which the reflective film 30 is not formed on the peripheral portion. The electrode layer 40 is continuously connected to the upper surface of the reflective film 30, the third exposed portion 21 of the insulating protective film 20, the second exposed portion 11 of the transparent conductive film 10, and the first exposed portion 5 of the contact layer 108. Is formed. As shown in the plan view of FIG. 2, when viewed from the direction perpendicular to the light emitting surface, the first exposed portion 5, the second exposed portion 11, and the third exposed portion 21 are annular staircases in the peripheral portion of the contact layer 108. It is formed in a shape. The electrode layer 40 is formed in a region indicated by hatching in FIG.

  Thus, since the insulating protective film 20 is interposed between the reflective film 30 and the transparent conductive film 10, the interface reaction between the reflective film 30 and the transparent conductive film 10 is prevented. Therefore, the transparency of the transparent conductive film 10 does not decrease, and the reflectance of the reflective film 30 does not decrease. Therefore, the amount of light incident on the reflective film 30 does not decrease and the reflectance of the reflective film 30 does not decrease, so that the light reflected to the translucent substrate 101 side can be increased.

  Furthermore, when a voltage is applied to the electrode layer 40 so that the electrode layer 40 has a positive potential with respect to the other electrode 140, for example, current flows in a direction perpendicular to the substrate 101 from the reflective layer 30. This is blocked by the insulating protective film 20. That is, most of the current is supplied to the transparent conductive film 10 from the peripheral portion of the electrode layer 40 via the annular second exposed portion 11. A part of the current flows from the peripheral portion of the electrode layer 40 to the transparent conductive film 10 via the side wall of the transparent conductive film 10 and is supplied to the contact layer 108 via the annular first exposed portion 5. As a result, there is no current flowing through the reflective film 30 in a direction perpendicular to the surface of the reflective film 30, so that electromigration of metal atoms in the reflective film 30 does not occur.

  If the same amount of current is supplied to the contact layer 108, the areas of the transparent conductive film 10 and the reflective film 30 should be as large as possible in order to improve the external quantum efficiency. Moreover, it is better not to form the 1st exposed part 5 or the 2nd exposed part 11 in this part on the relationship where light emission becomes strong on the side close to the other electrode 140. Considering this, it is also desirable to configure as shown in FIG. That is, the transparent conductive film 10 is formed in the same shape as the contact layer 108 and the first exposed portion 5 is not provided. Then, the insulating protective film 20 is formed inside the transparent conductive film 10 only on the right side A and the lower side B in the drawing of FIG. 3, and the second exposed portion 11 is formed in an L shape. . The insulating protective film 20 and the reflective film 30 are formed in the same shape, and the third exposed portion 21 is not provided. Then, the electrode layer 40 is formed in the same plane shape as the contact layer 108. At this time, the electrode layer 40 comes into surface contact with the transparent conductive film 10 at the L-shaped second exposed portion 11 located at the right end A and the lower end B in FIG. 3, and the current is transparent from the second exposed portion 11. It is supplied to the conductive film 10 and flows in the vertical direction to the lower contact layer 108 while spreading laterally in the transparent conductive film 10. By widening the transparent conductive film 10 in this manner, the light emitting portion can be widened, and by widening the reflective film 30, the reflection area toward the substrate 101 can be widened.

  Furthermore, as shown in FIG. 4, the second exposed portion 11 is not formed over the entire length of the right side A and the lower side B of FIG. 3, but only the length of ½ to ３ of each side from the apex. You may make it stop. In this case, the transparent conductive film 10, the insulating protective film 20, and the reflective film 30 are formed in a region where the second exposed portion 11 is not formed. Even if comprised in this way, an electric current will fully be supplied to the transparent conductive film 10 from the electrode layer 40 via the L-shaped 2nd exposed part 11, and another part is made into a light emission area | region and a reflection area | region. Therefore, external quantum efficiency can be improved.

  In addition, when the 1st exposed part 5 and the 2nd exposed part 11 are not formed in cyclic | annular form, even if those formation positions are the same, it is not necessary to make it the same. If the second exposed portion 11 is not formed at all, a current is supplied to the transparent conductive film 10 from the side surface. Light emission is possible even in this way, but if the second exposed portion 11 is provided, the contact area between the electrode layer 40 and the transparent conductive film 10 can be increased, so it is desirable to provide the second exposed portion 11. When the first exposed portion 5 is provided, it is possible to supply current from the side wall of the transparent conductive film 10, and thus the first exposed portion 5 is provided at the same position after the second exposed portion 11 is provided. This is desirable.

  Furthermore, as shown in FIG. 5, the reflective film 30 may be formed so as to be completely covered with the insulating protective film 20 from above and below, that is, in the insulating protective film 20. In this way, electromigration of the metal atoms of the reflective film 30 due to current can be completely prevented. Therefore, the reliability of the element can be improved.

  The method for forming the transparent conductive film 10 can be sputtering, vacuum deposition, or the like, and is not particularly limited, but is preferably formed by vacuum deposition using an electron beam. The insulating protective film 20 can be formed by sputtering, vacuum deposition, or the like, and is not particularly limited, but is preferably formed by plasma CVD. As a method for forming the reflective film 30 and the electrode layer 40, it is desirable to use sputtering or vacuum deposition.

The single quantum well structure and the multiple quantum well structure constituting the light emitting layer have a group III nitride compound semiconductor Al _y Ga _1-yz In _z N (0 ≦ y <1,0) containing at least indium (In). Those including a well layer of <z ≦ 1) are desirable. The structure of the light emitting layer includes, for example, a well layer made of doped or undoped Ga _1-z In _z N (0 <z ≦ 1), and a group III nitride having an arbitrary composition having a larger band gap than the well layer. Examples thereof include a barrier layer made of a physical compound semiconductor AlGaInN. Preferable examples are a well layer of undoped Ga _1-z In _z N (0 <z ≦ 1) and a barrier layer made of undoped GaN. Here, doping means that a dopant is intentionally included in the source gas and added to the target layer, and undoping does not intentionally add a dopant without including the dopant in the source gas. Means things. Therefore, undoped includes a case where it is naturally doped by diffusing from the adjacent layer.

  As a method for crystal growth of the III-V nitride compound semiconductor layer, molecular beam vapor phase epitaxy (MBE), metalorganic vapor phase epitaxy (MOVPE), hydride vapor phase epitaxy (HVPE), liquid phase epitaxy Laws are effective.

The group III-V nitride semiconductor of each layer constituting the semiconductor element is at least a binary system represented by Al _x Ga _y InN (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1), It can be formed of a III-V nitride compound semiconductor composed of a ternary or quaternary semiconductor. Some of these group III elements may be replaced by boron (B) and thallium (Tl), and part of nitrogen (N) may be phosphorus (P), arsenic (As), antimony (Sb ) Or bismuth (Bi).

  Further, when forming an n-type layer using these semiconductors, SiGe, Se, Te, C, etc. are added as n-type impurities, and when forming a p-type layer, a p-type impurity is formed. For example, Be, Ca, Sr, Ba, or the like can be added.

FIG. 1 is a cross-sectional view showing a semiconductor light emitting device 1 of Example 1, and FIG. 2 is a plan view thereof. A buffer layer 102 made of aluminum nitride (AlN) and having a thickness of about 20 nm is provided on a sapphire substrate 101 as a light-transmitting substrate having a thickness of 100 μm, and a film thickness made of silicon (Si) -doped GaN. An n-type contact layer 104 which is a high carrier concentration n ⁺ layer of about 8.0 μm is formed. The n-type contact layer 104 has an electron concentration of 5 × 10 ¹⁸ / cm ³ . The higher the electron concentration of this layer, the better, but it can be increased to 2 × 10 ¹⁹ / cm ³ . A strain relaxation layer 105 made of In _0.03 Ga _0.97 N is formed on the layer 104 to a thickness of 200 nm. Then, on the strain relaxation layer 105, a light emitting layer 106 having a multiple quantum well structure (MQW) formed by stacking three periods of non-doped GaN having a thickness of 20 nm and non-doped Ga _0.8 In _0.2 N having a thickness of 3 nm is formed. Has been. On the light emitting layer 106, a p-type layer 107 corresponding to a clad layer having a film thickness of about 60 nm made of magnesium (Mg) -doped Al _0.15 Ga _0.85 N is formed. Further, a p-type contact layer 108 made of magnesium (Mg) -doped GaN having a thickness of about 130 nm is formed on the p-type layer 107.

A transparent conductive film 10 made of ITO formed by MOCVD is formed on the p-type contact layer 108. A first exposed portion 5 is formed in a ring shape around the planar periphery of the p-type contact layer 108. An insulating protective film 20 made of SiO ₂ is formed on the transparent conductive film 10 so that the second exposed portion 11 is formed in the peripheral portion. The second exposed portion 11 corresponds to the exposed portion of claim 1. In addition, a reflective film 30 made of silver (Ag) is formed on the insulating protective film 20 so that an annular third exposed portion 21 is formed in the peripheral portion. Furthermore, an electrode layer 40 made of gold (Au) is formed so as to completely cover the first exposed portion 5, the second exposed portion 11, the third exposed portion 21, and the reflective film 30. The transparent conductive film 10 has a thickness of 0.5 μm, the insulating protective film 20 has a thickness of 200 nm, the reflective film 30 has a thickness of 0.5 μm, and the electrode layer 40 has a thickness of 1.2 μm.
The thickness of the reflective film 30 is preferably in the range of 0.01 to 5 μm from the viewpoint of light reflection, more preferably 0.02 to 2 μm, and most preferably 0.05 to 1 μm. The thickness of the transparent conductive film 10 is preferably 0.05 to 1 μm, and more preferably 0.2 to 0.5 μm, in view of electrical contact with the p-type contact layer 108.
The electrode layer 40 may be a double structure of titanium (Ti) having a thickness of 0.01 μm and gold (Au) having a thickness of 0.5 μm, or an alloy thereof. Or you may form in order of gold | metal | money and titanium and may cover it with protective films, such as a silicon oxide except the formation part of a pump.

  On the other hand, an n-electrode 140 is formed on the exposed n-type contact layer 104 by etching from the p-type contact layer 108. The n-electrode 140 has a double structure, and a vanadium (V) layer 141 having a thickness of about 18 nm and an aluminum (Al) layer 142 having a thickness of about 1.8 μm are partially exposed from the n-type contact layer 104. It is configured by sequentially laminating the portions.

  As shown in FIG. 2, the electrode layer 40 formed in this way is uniformly formed in an approximately 3/4 region on the upper surface of the p-type contact layer 108. The exposed portion of the electrode layer 40 and the exposed portion of the n-electrode 140 are connected to the bump.

  The light-emitting element 1 manufactured in this manner is compared with a light-emitting element in which a reflective film made of silver is formed on a transparent conductive film and an electrode layer made of gold is formed thereon without using an insulating protective film. The external quantum efficiency was improved by about 20%. Further, even after aging for 1000 hours, no decrease in external quantum efficiency was observed.

  The semiconductor light emitting device having the structure shown in FIGS. 3, 4, and 5 described in the preferred embodiment was manufactured, and the same effect as in Example 1 was obtained. 3, 4, and 5, the members denoted by the same reference numerals as those in FIGS. 1 and 2 are the same as the components described in the first embodiment and the preferred embodiment.

That is, FIG. 3 shows an element in which only the second exposed portion 11 is formed in an L shape on the right side A and the lower side B without forming the first exposed portion and the third exposed portion. The transparent conductive film 10 made of ITO was formed in the same plane shape as the p-type contact layer 108, and the insulating protective film 20 made of SiO ₂ and the reflection film 30 made of Ag were formed in the same plane shape. In addition, the electrode layer 40 made of Au was configured to be joined to the entire upper surface of the reflective film 30 and the second exposed portion 11. A current is supplied from the upper surface of the transparent conductive film 10 to the transparent conductive film 10 from the electrode layer 40 through the second exposed portion 11. The second exposed portion 11 corresponds to the exposed portion of claim 1. In the example of FIG. 4, the second exposed portion 11 is formed in an L shape in the range of about 1/3 to 1/2 of the right side A and the lower side B, and the other configuration is the same as the example of FIG. 3. This is an example. In the example of FIG. 5, the planar shape of each film is the same as that of the first embodiment shown in FIGS. 1 and 2, and the reflective film 30 made of Ag is completely replaced by the insulating protective film 20 made of SiO _2. This is an example of a covered configuration.

  In the light emitting devices having the configurations of the first and second examples, it is obvious that the materials of the films and layers described in the embodiment of the invention can be selected in any combination.

  The present invention can be used for light emitting devices such as light emitting elements, light emitting element chips, LED lamps, and displays. This is extremely effective in improving the external quantum efficiency of the light emitting device, and the light emission output can be increased if compared with the same input power.

Sectional drawing of the light emitting element concerning the specific Example of this invention. The top view of the light emitting element of the Example. The top view of the light emitting element concerning the other specific Example of this invention. The top view of the light emitting element concerning the other specific Example of this invention. The top view of the light emitting element concerning the other specific Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light emitting element 5 ... 1st exposed part 10 ... Transparent conductive film 11 ... 2nd exposed part 20 ... Insulating protective film 21 ... 3rd exposed part 30 ... Reflective film 40 ... Electrode layer 101 ... Sapphire substrate 102 ... Buffer layer 104 ... n-type contact layer 105 ... strain relaxation layer 106 ... light emitting layer 107 ... p-type cladding layer 108 ... p-type contact layer 140 ... n-electrode 150 ... p-electrode

Claims (7)

Light having a light-transmitting substrate and a semiconductor layer stacked on the light-transmitting substrate, and an n-electrode and a p-electrode formed on the semiconductor layer side with respect to the light-transmitting substrate and emitting light In a flip-chip type semiconductor light emitting device that emits light from the translucent substrate side,
A contact layer which is the uppermost layer of the semiconductor layer;
A transparent conductive film transparent to the light formed on the contact layer;
An insulating protective thin film formed on the transparent conductive film;
A reflective film having a high reflectivity with respect to the light made of metal formed on the insulating protective film;
An electrode layer formed on the reflective film and formed so as to be joined to a part of the transparent conductive film.   The transparent conductive film has an exposed portion where the insulating protective film is not formed on at least a part of its peripheral portion, and a part of the electrode layer is provided on the exposed portion. The semiconductor light emitting device according to claim 1.   The semiconductor light emitting element according to claim 1, wherein a periphery of the reflective film is covered with the insulating protective film. 4. The semiconductor light emitting device according to claim 1, wherein the transparent conductive film is made of indium tin oxide (ITO). 5. 5. The semiconductor light emitting device according to claim 1, wherein the insulating protective film is made of at least one of silicon oxide and silicon nitride. 6. The semiconductor light emitting element according to claim 1, wherein the reflective film is made of at least one of aluminum, silver, an aluminum alloy, or a silver alloy. The semiconductor light emitting element according to claim 1, wherein the electrode layer is made of gold, a multilayer film of gold and titanium, or an alloy of gold and titanium.